Question

why Himalayan rivers are called as perennial rivers

Answer 1

because they contain water throughout the year. They get water either through rain or by melting of glaciers in the mountains.

Answer 2

The Himalayan rivers are perennial rivers as they originate in snow covered Himalayan mountains. During summers, the snow melts and the rivers get continuous supply of water. On the contrary, the peninsular rivers depend mostly on rainfall for its supply of water and thus becomes dry during the summer seasons